Parking lock for an automatic transmission and method for operating the parking lock

Abstract

In a parking lock for an automatic transmission, an electrical parking lock actuator has an electric motor, a spur gear stage driveable by the electric motor, and a worm gear stage driveable by the spur gear stage. A worm shaft of the worm gear stage is connected rotationally conjointly to an output gear of the spur gear stage, and a worm gear of the worm gear stage is connected rotationally conjointly to a transmission-side parking lock shaft. The worm shaft is fixed in an axially displaceable manner in the output gear. A stop limits the pivoting movement of the worm gear when a parking lock position of the parking lock shaft is reached. A spring braces the worm shaft in an axial direction of the worm shaft against a holding mechanism which is situated in a stop position, in which the holding mechanism is fixed by an electrically energized electromagnet.

What is claimed is: 
     
       1. A method for operating a parking lock for an automatic transmission, the parking lock including an electric motor, a spur gear stage which is driveable by the electric motor, and a worm gear stage which is driveable by the spur gear stage, said method comprising the steps of:
 A. during a disengagement of a parking lock, a worm shaft of the worm gear stage, which is supported via a holding means on an electromagnet, is rotated in a forward direction of rotation when the electromagnet is electrically energized, 
 B. during engagement of the parking lock, the worm shaft, which is supported on an output gear of the spur gear stage, is rotated in a backward direction of rotation, 
 C. wherein in the case of an electrical failure resulting in an electrically deenergized electromagnet and interrupted action on the holding means, and when the parking lock is disengaged, the worm shaft is displaced axially under the action of a spring, with a worm gear of the worm gear stage simultaneously being pivoted in order to engage the parking lock. 
 
     
     
       2. The method as claimed in  claim 1 , wherein, in method step A, the electromagnet is electrically energized to a maximum extent, or, when the parking lock is disengaged, the electromagnet is electrically energized to a reduced extent, or, in method step B, the electromagnet is electrically energized to a reduced extent. 
     
     
       3. The method as claimed in  claim 1 , wherein, in the case of a reset function after the electrical failure and in the event of a renewed supply of electricity, the electric motor rotates the worm shaft backward, the worm shaft moves in a direction of the output gear into an initial position, the spring moves the holding means against the electromagnet, and the electromagnet is electrically energized. 
     
     
       4. The method as claimed in  claim 3 , wherein the electromagnet is electrically energized to a reduced extent.